Scores of people were killed and tens of thousands left homeless in central Italy today after a powerful earthquake shook a mountain region, severely damaging a historic city and leaving hundreds feared trapped in rubble.

At least 92 people were known to have died, the Italian news agency Ansa reported, quoting local rescue workers, while the Red Cross said it faced a "race" to rescue those still trapped.

More than 1,500 people had been injured, the Italian prime minister, Silvio Berlusconi, told a press conference in L'Aquila, the badly damaged capital of the Abruzzo region, close to the quake's epicentre.

Berlusconi declared a state of emergency, calling off a scheduled trip to Russia to co-ordinate the government's response. "I want to say something important: no one will be abandoned to their fate," he told reporters.

The 6.3-magnitude tremor, which struck at 3.32am local time (2.32am BST), was the country's deadliest since the Irpinia quake in the south in November 1980, which killed more than 2,500 people.

More than 1,000 rescue workers were this afternoon scrambling to reach those trapped in collapsed buildings.

"We will work for the next 48 hours without any stop, because we have to save lives," Francesco Rocca, the head of Italy's Red Cross, told BBC television. "We estimate that hundreds of people could still be alive under the buildings." It was now "a race" to save those trapped, he added.

Up to 50,000 people may have been left homeless by this morning's quake, a spokesman for Italy's civil protection agency said. The need for shelter is all the more urgent in a region where night-time temperatures remain just above 5C (41F).

Tens of thousands of tents, along with field kitchens and mobile hospital units, were being rushed to the region. Neighbouring countries offered assistance, and the US president, Barack Obama, was among the first to send his condolences.

L'Aquila, with a population of around 70,000, has been left in a state of chaos, with dozens of buildings collapsed and many others – newer blocks included – left with jagged tears down the walls. After the Irpinia quake in 1980, construction codes were introduced that were intended to ensure all modern buildings could withstand tremors.

Berlusconi said he had noted the number of damaged modern buildings while surveying the disaster area by helicopter.

A thick layer of pale dust thrown up by the shaking covered every surface. "The situation is terrible, really terrible," said the city's mayor, Massimo Cialente, adding that he had "shed some tears".

As a series of strong aftershocks jolted the region, thousands of local people began to flee, many on foot, draped in blankets to ward off the cold and carrying suitcases. Long queues formed at petrol stations.

Some surrounding villages, where a greater proportion of homes were older, are feared to have fared even worse. People in Tempera, a few kilometres east of L'Aquila, told the Guardian that virtually every house in the historic village centre had been flattened, with many people feared dead.

"The quake was so strong. I was woken from my bed and when I tried to get up I fell over," one man said. As a construction worker with access to building equipment he had helped with rescue efforts, and had so far helped remove 10 bodies from the rubble, he said.

A witness in Paganica, close to Tempera, said the village "looks as if it has been bombed".

Rescue efforts were hampered by rubble blocking roads. At the site of one four-storey apartment block in L'Aquila, now collapsed to a height of about two metres, emergency workers clawed away chunks of rubble with their hands to try to reach at least four people believed to be trapped inside.

"I woke up hearing what sounded like a bomb," said Angela Palumbo, 87, as she took shelter on the streets. "We managed to escape with things falling all around us. Everything was shaking, furniture falling. I don't remember ever seeing anything like this in my life," she told Reuters.

Among the damaged buildings was a student residence in L'Aquila, a popular student city. "We managed to come down with other students but we had to sneak through a hole in the stairs as the whole floor came down," said one student, Luigi Alfonsi, 22. "I was in bed. It was like it would never end as I heard pieces of the building collapse around me."

Dozens of injured people were waiting outside the city's main hospital, which was only partly open after suffering damage, according to local reports. Another hospital was closed owing to fears for its structural safety, and those most seriously hurt were being flown by helicopter to other cities.

The last significant Italian earthquake was in 2002, when 27 children and one adult died after a school collapsed in Molise, in the south of the country.